Orthodontic problems, including craniofacial anomalies, are extremely prevalent in our society and can often be severely debilitating. Orthodontic procedures are based on stimulating predictable bone remodelling patterns in periodontal tissues by applying stresses of known vectors and magnitudes. The primary thrust of this research is directed toward isolating and identifying the molecules which cause the bone resorption stimulated in the tissues surrounding stressed teeth and clarifying their mechanisms of action. With the recognition and general acceptance of the importance of the role(s) played by prostaglandins and collagenase in bone resorption, as well as defense mechanism against bacterial invasion and injury, these studies will emphasize the relative importance of these molecules as they relate to mechanisms of orthodontically-induced bone resorption. Such an understanding is necessary to progress toward more rational approaches to treatment and the prevention of the unwanted sequelae of treatment.